In an allelotyping study of prostatic carcinoma, we found the highest frequency of allelic deletions on chromosomes 8, 10, 16, and 18. In all cases with allelic deletions, at least one of the chromosomes 8, 10, and 16 were involved. A detailed deletion mapping of these chromosomes in I 8 cases was carried out with probes that detect restriction fragment length polymorphisms (RFLP) on chromosomes 8 (6 probes), I 0 (I I probes), and I6 (9 probes). The highest frequency of allelic deletions were found on 8p (65%). where the minimally deleted region was between the PLAT locus and pter. The long arm of chromosome I6 had allelic deletions in 56% of informative cases, with three different break points, the most distal being located between D I6S4 and D I6S7. Chromosome I0 exhibited a complex deletion pattern with terminal deletions of the p or the q arm (2 cases each), a deletion pattern that could be interpreted as nonreciprocal translocations of the q arm (2 cases), o r allelic losses on all informative loci, suggesting monosomy (2 cases). Our data suggest that tumor suppressor genes involved in the oncogenesis of prostatic carcinoma may be localized between 8 pter and the PLAT locus and that additionaValternative tumor suppressor genes may be localized on chromosome 10 and on the long arm of chromosome 16 distal t o the D16S4 locus.